1. Field of the Invention
The present invention relates to a novel ionically conductive macromolecular material used for electrolytes or electrodes. It concerns, in particular, materials which are present in the form of a polyether-salt based network and/or polycondensate.
2. Discussion of the Background
Such ironically conductive macromolecular materials are either not crystalline, or only very slightly crystalline, at ambient temperature. Therefor it is practically impossible to utilize them to produce electrochemical current generators, whether they be primary or secondary.
According to the prior art, solid electrolytes constituted by solid solutions of ionic compounds in polymers are already known. Reference may be made, for example, to European Pat. No. 0 013 199, entitled "Generateurs electrochimiques de production de courant et nouveaux materiaux pour leur fabrication which describes solid solutions of lithium salts in polar aprotic solutions capable of solvating the cation. These solutions constitute solid electrolytes that can be utilized in thin layers in solid generators. Among the polymers cited in this European patent ethylene polyoxides, propylene polyoxides and their copolymers are cited in particular.
In order to improve the mechanical properties of the electrolytes thereby constituted, and their behaviour with respect to crystallization, French patent application published under No. 2 485 274 entitled "Electrolyte solid a base de materiau macromoleculaire a conduction ionique" proposes to utilize as the electrolyte a cross-linked polymer complex material. The cross-linking is carried out with polymers containing hydroxyl functions that can be cross-linked by isocyanates, which leads to urethane networks in which the said functions are capable of reacting with the elements of the anode and/or the cathode and thus to provoke on the one hand a degradation of the polymer which could thus no longer fulfill its role of elastomer binder, and parallely on the other hand the consumption of a portion of the cathode or anode materials through irreversible oxidation.
The products obtained according to this cross-linking method present, due to the large dimension of the knots or meshes of the network initiated by the isocyanates, a high volumic (or massic) percentage of non solvating portion of the cation that can hinder the dissolutions and/or the dissociation of the salt, thereby causing a decrease in conductivity. If it is desired to overcome this poor solvation, it is possible to increase the molecular weight of the functional starting polymer but this generally leads to a decrease in the ionic conductivity of the polyether-salt complex through crystallization at low temperature.